Vintage Mustang Forums banner

1 - 19 of 19 Posts

·
Registered
Joined
·
28 Posts
Discussion Starter #1
Check this out. Several months ago I was getting onto the freeway, I accelerated quickly to get up to speed, and heard a bad, bad POP sound. The engine was still running, but it sounded like it was missing part of the header.... Anyway, I towed the car home where it has sat while I have been pissed. I thought maybe I had damaged a head, but I really had no idea since I do not really know what I am doing when it comes to trying to be a mechanic. So, today I finally popped of the valve cover to see this:
http://memimage.cardomain.net/member_images/10/web/766000-766999/766266_36.jpg
http://memimage.cardomain.net/member_images/10/web/766000-766999/766266_37.jpg
http://memimage.cardomain.net/member_images/10/web/766000-766999/766266_38.jpg

The strange thing is, this is the second time I have had valve train issues at this cylinder. A couple of years ago, while trying to diagnose a performance issue I pulled off this valve cover to find a broken rocker arm stud. I replaced all of the rocker arm studs only to find some damage to all of them. Very, very low mileage. I think the damage to the rest of the studs was due to the bolts not being secured properly causing excessive wear. But now, I wonder what is going on. Thoughts? How should I proceed?
 

·
Registered
Joined
·
9,896 Posts
I see aftermarket parts, so I'm going to assume that you have an aftermarket cam. It doesn't take an awful lot of abuse to break a factory cast rocker arm, a stuck valve will do the job, as will excessive lift causing the springs or rockers to bind. I would spend some time ensuring that all your clearances are properly set, check for coil bind, etc.
 

·
Registered
Joined
·
7,032 Posts
Maybe it's just the picture (or my eyes!), but where's the oil? I don't see any oil residue in that picture.
 

·
Registered
Joined
·
28 Posts
Discussion Starter #4
.501 lift. If that helps.
 

·
Registered
Joined
·
28 Posts
Discussion Starter #5
It seems to oil fine. Not sure what fine is I guess, but there is oil pooled in the head, and I saw all of the push rods oiling after I changed the rocker arm studs.
 

·
Premium Member
Joined
·
7,773 Posts
Obviously check for a stuck valve. But, my suggestion would be to upgrade your rocker arms. You mentioned that you replaced your studs, same deal here. There's a huge difference in quality there.

-bob
 

·
Premium Member
Joined
·
5,242 Posts
Hemikiller's right on the nose. You've got aftermarket parts there, including a higher lift cam, working on a 40 year old piece of metal that's under constant stress. Its a small part(s) that too often is overlooked when performance cams, etc. are added to ooolllld engines.
Good excuse to replace them all now!
Good luck with it.
 

·
Registered
Joined
·
295 Posts
.501 lift. If that helps.
I might be wrong on this but Isn't that a real high lift cam? Doesnt the ratio of the rockers change with that size cam? Are the pushrods a bit too long? Just throwing this out there, I don't realy know what I am talking about and maybe I should keep my mouth shut.
 

·
Registered
Joined
·
1,425 Posts
My cam is .496 .520 and stock legnth push rods were recommended for that lift
 

·
Registered
Joined
·
7,295 Posts
Maybe it's just the picture (or my eyes!), but where's the oil? I don't see any oil residue in that picture.
I tend to agree - I see a bit of oil on the inverted hex head plug - but otherwise it does look pretty non-oiled IMO too.
 

·
Registered
Joined
·
316 Posts
If you are confident that the valves were adjusted properly, check for adequate clearance between the spring retainer and rocker arm. With larger aftermarket retainers and camchafts, the retainer can come in cantact with the rocker. Check carefully during a complete valve cycle. Also, make sure you are using the correct length push rod for you combination. Check Comp Cams or Crane's website on how to check. Something is up as the stock rocker should not break. This is the same rockers that were used in solid lifter hipo K motors. Something is wrong with your setup to break your rockers. Aftermarket units are the way to go, but fix your problem first, otherwise you will be breaking an expensive set of rockers.

Oscar
 

·
Registered
Joined
·
1,963 Posts
.501" lift should not be enough to cause coil bind. But since you already have the valve cover off, it's easy enough to check. Also, if your springs are new and you have the receipt you can reference the part number and look up their specs to find the lift at which they bind.

Since you have everything installed you can check for bad geometry by turning over the engine and watching one of your rockers. As a lifter rides up on the cam lobe the tip of the rocker travels across the valve stem. At the fully closed position the tip of the rocker should be sitting slightly outboard of the center of the valve stem. At fully open position it should be slightly inboard. These two extremes should be roughly equal to each other. If they're not, you can correct the problem with longer or shorter pushrods.

The other geometry issue is rocker-to-retainer interference. This happens at the fully closed position. If you've got visible space between the rocker and the valve retainer when the valve's fully closed, you don't have this problem. Again, the cure is custom length pushrods.

I doubt if you have coil bind or geometry problems, since a .501" lift indicates a fairly mild cam. But they're easy to check.

As far as some problem with the studs, I don't understand the statement about how the rocker studs could have been damaged because the bolts were not secured properly. What bolts?

Anyway, guessing that what you mean is that you have screw-in studs and they weren't screwed in tight and you've corrected that problem, it seems like that would not be a factor in the rocker breakage. I think it was just time for that part to go. You know at 3000 rpm a valve opens and closes 1500 times per minute, or 90,000 times per hour. Multiply 90,000 by how many hours your engine has been running, and you can see that a 40 year old rocker has been through a lot.
 

·
Registered
Joined
·
1,839 Posts
If you end up replacing your rockers consider roller tip rockers. Not much cost difference over regular rockers and no other changes like valve covers are needed.
 

·
Registered
Joined
·
577 Posts
Are the slots in the rocker arm(s) long enough to allow for the extra lift?
 

·
Registered
Joined
·
6,782 Posts
TRW rocker arms? Guess where they are made: CHINA. That is my guess. I have had two of them break in my engine's 15 year life (since rebuild) and I have a much milder cam than you.

I think there still may be time to ask for a nice set of roller rockers from Santa...
 

·
Gone but never forgetten
Joined
·
25,239 Posts
.501" lift should not be enough to cause coil bind.
I disagree, Bill. .501 is PLENTY to cause coil bind and snap a rocker ... been there, done that, got the T-shirt.

On the engine that is now in my daughter's '69 (it used to be in my '66), I fired it up with an Edlebrock RPM cam and stock springs. It took all of about 30 seconds to snap a rocker arm.
 

·
Registered
Joined
·
1,844 Posts
Are the slots in the rocker arm(s) long enough to allow for the extra lift?
This was going to be my question. It explains the damage to all of the rocker studs and the broken rocker arm. I have had this problem before on other people's cars and I had to elongate the slots with a die grinder to prevent the rocker arms from binding once a larger lift cam was installed.
 

·
Registered
Joined
·
9,896 Posts
.501" lift should not be enough to cause coil bind.
I disagree, Bill. .501 is PLENTY to cause coil bind and snap a rocker ... been there, done that, got the T-shirt.

On the engine that is now in my daughter's '69 (it used to be in my '66), I fired it up with an Edlebrock RPM cam and stock springs. It took all of about 30 seconds to snap a rocker arm.
Not only is it enough to bind a stock spring, it is enough to put the retainer in contact with the valve guide. (It was only .440" on a 351W I did some work on once) Check both of those clearances on all cylinders. You may also have a rocker slot problem, since you noted that all of your studs were damaged previously....
 
1 - 19 of 19 Posts
Top